To get this Trophy you must play Number Ball, a mini game in which you must touch the number balls in the correct order from 1 to 50. The number balls (think pool balls) bounce around the screen and get quicker as the timer counts down.
Each ball is the same colour each time you play!
This means that you can write down the number and colour for each ball and then follow your guide in order to get all 50 within the allotted time.
The faster you get each one the easier it is to get the next and thus you can easily get the 50 within the time limit.